Blue happens when there is an absence of red pigment. Some breeders try for them - Nocturnals for one. I think there was a move towards 'mahogany' too, a couple of years back.
New puppy people and breeders
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http://www.patriciamcconnell.com/product/the-puppy-primer
Dr McConnell has a revised book out for those of you who have new puppies. I have not read this one, but based on the books of hers that I have read, I do not hesitate to suggest this one.
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I sent the earlier version of this book home with my puppies last year. I think it is a good addition to a new puppy owner's library.